Social Data Commons: Housing + Transportation Affordability (v3.1.3)

Overview

Housing and transportation affordability index independently reproduced using the Center for Neighborhood Technology (CNT) H+T Index methodology. Combines housing costs with modeled transportation costs (auto ownership, vehicle miles traveled, and transit use) as a percentage of household income for a Regional Typical Household. Transportation costs are derived from three regression models with 17 independent variables computed from ACS demographics, LEHD employment data, TIGER geographic boundaries, and GTFS transit schedules at block group resolution. This dataset is produced by the Social Data Commons at the University of Virginia as part of the Affordability Index data pipeline.

Provenance

Independently reproduced using the methodology published by the Center for Neighborhood Technology (CNT). Regression coefficients from CNT Tables 3-6 are applied to 17 independent variables computed from American Community Survey data, LEHD Origin-Destination Employment Statistics, TIGER geographic data, and GTFS transit feeds. Block group estimates are aggregated to tract and county via unweighted means.

Coverage

Temporal coverage: 2015–2024 (annual, ACS 5-year + GTFS + LEHD)

Geographic levels: Block Group, County, Tract

Coverage areas: National Capital Region (DC metro), Virginia (statewide)

Methodology

The Housing + Transportation (H+T) Affordability Index measures the true cost of housing by combining housing and transportation costs as a percentage of household income. A neighborhood is considered affordable when H+T costs consume no more than 45% of household income. This measure uses the Regional Typical Household variant, which reflects a household earning the regional median income. Reproduced independently using CNT's published regression coefficients (Tables 3-6) applied to ACS demographic data, LEHD employment data, and GTFS transit schedule data at block group resolution.

Annual housing cost (weighted average of median owner costs and gross rent by tenure ratio) as a percentage of the regional median household income. Part of the H+T Affordability Index decomposition.

Annual transportation cost (auto ownership + vehicle miles traveled + transit use) as a percentage of the regional median household income. Derived from CNT regression models for auto ownership, VMT, and transit ridership applied to neighborhood-level variables.

Predicted automobile ownership per household from the CNT auto ownership regression model. Uses household income, density, transit access, employment gravity, and housing stock characteristics as predictors.

Predicted annual vehicle miles traveled per household from the CNT VMT regression model. Reflects how neighborhood density, transit access, employment access, and housing patterns influence driving behavior.

Predicted fraction of commuters using public transit from the CNT transit use regression model (quasibinomial). Reflects how transit connectivity, employment access, density, and household characteristics influence transit ridership. Block groups with no transit service are assigned 0%.

Source Tables

H+T Affordability Index Methods

U.S. Census Bureau

Mobility Database

H+T Affordability Index Methods, Table 4

H+T Affordability Index Methods, Table 5

H+T Affordability Index Methods, Table 6

Variables

B19013_001: Median Hh Income

B11001_001: Total Hh

B25003_002: Owner Occupied

B25003_003: Renter Occupied

B25003_001: Total Occupied

B25024_002: Units 1 Detached

B25024_001: Total Units

B08301_001: Workers 16Plus

B08301_003: Workers Drove Alone

B08301_004: Workers Carpool

B08301_010: Workers Transit

B08301_019: Workers Walked

B08301_020: Workers Other

B08301_021: Workers Wfh

B25008_001: Pop In Occ Hu

B01003_001: Total Pop

B25088_002: Median Owner Cost

B25064_001: Median Gross Rent

B25009_002: Hh Size Owner

B25009_010: Hh Size Renter

Measures (6)

Note on naming conventions: Measures containing _geo20 are reported on 2020 Census tract boundaries. Pre-2020 estimates are standardized from 2010 to 2020 census tract boundaries using an area-based crosswalk: intensive measures (rates, percentages, medians, per-household quantities, densities, and composite indices) are assigned the value of the area-dominant 2010 tract rather than area-averaged, so the measure's scale is preserved.

affordability_index_geo20: Housing + Transportation Affordability Index (mean, unit: percent) Proportion of income spent on combined housing and transportation costs for a Regional Typical Household.

housing_cost_pct_geo20: Housing Cost as Percent of Income (mean, unit: percent) Housing cost as a percentage of income for a Regional Typical Household.

transport_cost_pct_geo20: Transportation Cost as Percent of Income (mean, unit: percent) Transportation cost as a percentage of income for a Regional Typical Household.

autos_per_hh_geo20: Predicted Autos per Household (mean, unit: vehicles) Predicted number of automobiles per household based on neighborhood characteristics.

vmt_per_hh_geo20: Predicted Annual Vehicle Miles Traveled per Household (mean, unit: miles) Predicted annual vehicle miles traveled per household based on neighborhood characteristics.

transit_frac_geo20: Predicted Transit Commuter Fraction (mean, unit: percent) Predicted fraction of commuters using public transit based on neighborhood characteristics.

Data Sources

Center for Neighborhood Technology

American Community Survey 5-Year Estimates

LEHD Origin-Destination Employment Statistics

General Transit Feed Specification (GTFS)

File Format

Data files are provided as CSVs (.csv) with the following columns: geoid, year, measure, value, moe (margin of error, where available), region_type, data_method (observed, modeled, scaled, interpolated, or extrapolated). Per-measure metadata (descriptions, units, and sources) is documented in the dataset's measure_info.json in the Social Data Commons repository.